Abstract
In order to determine the cholinoceptive mechanism associated with cutaneous inhibition of jaw-closing and lumbar motoneurons, the area related to the inhibition produced by stimulation of the superficial radial nerve was identified by a lesion within the pontomedullary reticular formation and effects of drugs upon neurons were studied within this area. The cutaneous inhibition, as tested by the inhibition of monosynaptic reflex activity of jaw-closing and that of hindlimb spinal motoneurons was completely abolished by lesion of the medial portion of the pontomedullary reticular formation, but was little affected by lesions of the lateral portion. Intravenously administered physostigmine (0.15-0.30 mg/kg) excited 11 of 21 neurons whereas electrophoretic ACh (90 nA) excited 26 and inhibited 4 of 96 brainstem neurons located in this area. Eight of 11 physostigmine, and 4 of 26 ACh excited neurons were reticulospinal neurons with axonal conduction velocities of 20-40 m/sec. From results presented here together with those reported previously, these physostigmine sensitive and ACh excited brainstem neurons, reticulospinal and non-reticulospinal neurons, could be cholinoceptive interneurons of the polysynaptic inhibitory pathway, from the superficial radial nerve to jaw-closing and hindlimb spinal motoneurons.
